These twelve secrets are all the interiors of twelve blocks in the main area of the map. They will all be ordered according to where they are in a grid. The first block is the leftmost block, and the last block will be the rightmost block. There are four rows, top to bottom; and three blocks in each row: first, middle, and last. Note that three of these are necessary to get the three keys to leave the map.

First block, first row: Use the wall at the northeast corner. Grabbing the blue key here will make some shotgun guys teleport in. (sector 128)